Their geography dictates that they do not have alot of land use, particularly in terms of population per (mile, kilometer, foot, etc) which is extremely large, for anything but manufacturing plants.
To complement their land availability, their natural resources are not as sufficient as they could like. Fishing is big, and used in trade, but they do not hold any natural resources of suitable quantity and that could be produced efficiently (by all this I mean Comparative Advantage) that is far better than other countries. They could sell rice crop, but it wouldn’t be of a large enough scale (bulk shipping) to be worth buying like China has.

So they had to think, and think hard. With their large population on such a small landmass, and their low quantity of natural resources, they can utilise what little land they have to build big hulking manufacturing plants that sell cars and toys and other merchandise that is wanted all over the world. And because that is really their only effective means of production of their resources, they can invest millions and billions into that resource thereby giving them a great comparative advantage over other countries of whom have to invest money into their wide range of resources.

Climate really is of no concern in my explanation. It merely is another leverage that says they have to manufacture to withstain an economy.
In terms of their Economy itself, well I can’t say how their labor force is, if its like China’s or not. But with so many factories, I take it there are alot of businessmen in the crowds. But their Economy is nearly entirely manufacturing sufficient so unless another country comes by with a greater means of production, the Japanese Economy won’t collapse and burn.